This invention relates to an apparatus and to a method for operating an internal combustion engine, and in particular an apparatus and method for operating and controlling an internal combustion engine so as to reduce or substantially eliminate free oxygen contained in the exhaust gas produced by the engine.
A number of different industrial applications require the availability of a stream of gas that is either devoid of any free oxygen gas content, or that contains only minimal or trace amounts of oxygen gas. The elimination of free oxygen from a gas stream is often required in order to minimize corrosion and/or to minimize the potential for fire and explosion. For example, in the drilling of oil and gas wells, a stream of pressurized gas is often circulated from the surface down through the drill string to the drill bit to control sub-surface pressures, to carry cuttings and other debris from the bottom of the well bore to the surface, and in some instances to xe2x80x9cpowerxe2x80x9d a downhole motor used to drive a drill bit. To minimize the potential for fire, explosion, and the corrosion of metal components, such gases ideally have no free oxygen content. A stream of gas that is substantially devoid of free oxygen may also be required for underground reservoir pressure maintenance or for purging, pigging or testing piping and conduits.
Depending upon the particular industrial application, a variety of different sources of gas having no (or only trace amounts of) free oxygen may be utilized. For example, in the medical, food preparation, and microchip manufacturing industries where a highly pure and inert source of gas may be required, pressurized vessels containing nitrogen or other similar gas are often utilized. In other applications where the primary concern is that there be either no or only trace amounts of oxygen present in the gas, others have suggested the utilization of the exhaust gas stream from an internal combustion engine, particularly where remote locations or environmental issues are involved. Utilizing the exhaust gas stream from an internal combustion engine at a remote facility removes the necessity of transporting pressurized vessels of inert or oxygen-free gas over great distances, and also removes the associated cost. The use of the exhaust from an internal combustion engine as a source of such gas is particularly attractive in the drilling of oil and gas wells where the existence of combustion by-products is normally of little concern, or could even be beneficial.
Typically the intake air that is drawn into an internal combustion engine and utilized during the burning of hydrocarbon fuels will have a substantial portion of its free oxygen eliminated by means of the combustion process. Increasing the amount of fuel that is burned in the engine tends to increase the amount of free oxygen that is eliminated from the exhaust stream. Put another way, increasing the amount of fuel tends to decrease the amount of free oxygen that will be present in the engine""s exhaust. As the amount of fuel is increased there will become a point at which the amount of fuel present within the engine""s cylinders is sufficient such that all of the fuel reacts with all of the free oxygen present in the intake gas (the stoichiometric point) so that there will be complete combustion with the resulting exhaust gas stream substantially devoid of any free oxygen content. Unfortunately, to reach that point of complete combustion, the engine temperature that is achieved will typically far exceed the maximum operating temperature that standard internal combustion engine can safely handle. Further, at elevated operating temperatures internal combustion engines tend to create large amounts of nitrogen oxides and related compounds that are generally undesirable, and that may necessitate the implementation of additional processing steps downstream. For these reasons internal combustion exhaust gas systems that are currently available are generally designed to operate at a fuel-to-air mixture that allows the internal combustion engine to run below a level of complete combustion, and at or slightly below the engine""s maximum operating temperature. Operating the internal combustion engine in this range will prevent damage to the engine through overheating, and will help to limit the production of nitrogen oxides while creating an exhaust gas stream having a reduced amount of free oxygen.
While it will be appreciated that while the amount of oxygen in the exhaust gas stream will be reduced, there will nevertheless still be an oxygen gas component within the engine""s exhaust. Where small or trace amounts of free oxygen are unacceptable, the exhaust gas stream must be subjected to further processing to remove any remaining oxygen. Such further processing often involves xe2x80x9cburningxe2x80x9d any remaining oxygen within a catalytic converter or subjecting the exhaust gas to further chemical processing steps.
The invention therefore provides an apparatus and a method for operating an internal combustion engine that reduces the free oxygen content within the engine""s exhaust, that permits the engine to be operated within its maximum recommended operating temperature, that reduces nitrogen oxides, and that may eliminate or reduce the need or extent to which the exhaust gas stream need be subjected to further downstream processing to remove any remaining free oxygen content.
Accordingly, in one of its aspects the invention provides a method of controlling the operation of an internal combustion engine to reduce the presence of free oxygen in the exhaust gas of the engine, the method comprising operating the internal combustion engine with a fuel-to-air ratio in excess of the stoichiometric ratio such that the exhaust gas from the internal combustion engine is devoid or substantially devoid of all free oxygen and excess unburned hydrocarbon fuel is expelled with the exhaust gas from the engine.
In a further aspect the invention provides an apparatus for controlling the performance and operation of an internal combustion engine to reduce the presence of free oxygen within the exhaust of the engine, the apparatus comprising a fuel-to-air ratio controller, said fuel-to-air ratio controller regulating the fuel-to-air mixture within the intake of the internal combustion engine such that the fuel-to-air ratio is maintained in excess of the stoichiometric ratio with the exhaust gas from the internal combustion engine devoid or substantially devoid of all free oxygen and excess unburned hydrocarbon fuel expelled with the exhaust gas from the engine.
In yet a further embodiment the invention provides a method for providing a stream of substantially oxygen free gas for use as a drilling fluid in the underground drilling of a wellbore, the method comprising the steps of, operating an internal combustion engine with a fuel-to-air ratio in excess of the stoichiometric ratio such that the exhaust gas from the internal combustion engine is devoid or substantially devoid of all free oxygen content; collecting the exhaust gas from the internal combustion engine and directing the exhaust gas to a compression stage where the exhaust gas is compressed to a desired pressure; and, directing said pressurized exhaust gas that is devoid or substantially devoid of any free oxygen content to the wellbore for use in the drilling process.
Further advantages of the invention will become apparent from the following description taken together with the accompanying drawings.